This invention relates to gas sensors and more particularly to a gas sensor in which single crystal SnO micro-disks form the sensing element.
The increase in harmful gas emissions and the resultant threat to public health, particularly in urban environments, has stimulated research aimed at the development of highly sensitive and selective gas sensors suitable for air-quality monitoring [1]. NOx, CO, H2S are considered particularly harmful to public health, even at low concentrations, given their negative impact on the human respiratory system [2,3]. Detection of these pollutant gases at ppm and ppb levels, with high sensitivity and selectivity, remains a major challenge [4]. While there are a number of means for detecting gases based on optical, gravimetric and electrical approaches, those based on monitoring changes in resistance of semiconducting oxides upon surface adsorption/desorption of gases (chemoresistance) offer key advantages including low cost processing, simple design and measurement, coupled with relatively high sensitivity [5,6,7,8,9].
SnO2 has been the most highly investigated material in this class of sensors [10]. This research has included investigation of different fabrication approaches to form thin films[11], nano [12,13,14], mesoporous [15], and macroporous structures[16,17], as well as the impact of various catalysts and dopants on sensor response [18,19,20]. To achieve higher sensitivity and selectivity, more complex multilayered and metal functionalized structures based on SnO2 have been reported [21,22,23]. Despite these efforts, it has been difficult to obtain simple devices which combine high sensitivity and selectivity with long-term stability.